Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2012 Commitments to Extend Credit [Member]	Dec. 31, 2011 Commitments to Extend Credit [Member]	Dec. 31, 2012 Commitments to Extend Credit [Member] Minimum [Member]	Dec. 31, 2012 Standby Letters of Credit [Member]	Dec. 31, 2011 Standby Letters of Credit [Member]	Dec. 31, 2012 Loan Origination Commitments [Member]	Dec. 31, 2011 Loan Origination Commitments [Member]	Dec. 31, 2012 Loan Origination Commitments [Member] Real Estate Residential Loans [Member]	Dec. 31, 2011 Loan Origination Commitments [Member] Real Estate Residential Loans [Member]
Loss Contingencies [Line Items]
Number of months in which the majority of loan commitments are expected to fund loans	3 months
Face amount of off-balance sheet liability			$ 740	$ 677		$ 43	$ 46	$ 203	$ 145	$ 48	$ 30
Expiration period of commitments to extend credit			1 year		5 years
Face amount of off-balance sheet liability with expiration greater than five years			47
Reserve for unfunded commitments						0.3
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating leases, future minimum payments due - 2013	6.4
Operating leases, future minimum payments due - 2014	3.3
Operating leases, future minimum payments due - 2015	2.9
Operating leases, future minimum payments due - 2016	2.0
Operating leases, future minimum payments due - 2017	1.5
Operating leases, future minimum payments due - 2018 and thereafter	2.8
Consumer Price Index increase	3.00%
Operating lease rent expense	$ 10.8	$ 9.2